Land Surface Heterogeneity

Project S4 will assess and reduce the uncertainties of climate models caused by non-resolved subsurface processes, surface heterogeneity and its feedback to the atmospheric boundary layer (ABL) including cloud development and convection initiation. Using the HD(CP)² framework, the project will analyse the true impact of the land including sub-surface, vegetation and anthropogenic structures including its variability and change on the regional climate of central Europe with a focus on cloud and precipitation development, intensity, and distribution. Questions that will be assessed are:

What is its impact on cloud and precipitation development?

What is the effect of catchment-scale circulations, which evolve in structured terrain, on clouds and precipitation and on the local and regional climate including wind extremes and fog development?

How different was our climate before humankind started to dominate the landscape, and what part did related land surface changes ranging from deforestation to water management and urban development actually play in this?

The scientists in S4 will answer these questions following an extended validation of the ICON-LEM with state of the art land models that include a consistent representation of the terrestrial water and energy cycle. Finally, appropriate methods will be developed to bring the findings back to the ICON-NWP/GCM model development.

The figure shows the structure of the S4 project and how the individual work packages are related.

Work package 2 addresses the consistent simulation of water and energy fluxes at the land surface focusing on agricultural landscapes and their interaction with the evolution and the thermodynamic structure of the atmospheric boundary layer (ABL).

As we know, topography and related land-use patterns will result in catchment-scale circulation patterns, for example, valley winds, cold pools, fog and so on. These circulations are not only impacted by the aforementioned effects but also by soil moisture variations which are caused by groundwater flow and convergence along river corridors. In work package 3, we will try to answer how catchment-scale heterogeneity and induced circulations impact boundary-layer, cloud, and precipitation development.

A key role in the process chain from land-surface variations, Atmospheric Boundary Layer (ABL) heterogeneity and convection is played by ABL-troposphere coupling - a process that occurs on different scales. In workpackage 4 we will provide a better understanding of this coupling, which is important for a better estimation of the occurrence and strength of convection and its influence on heavy precipitation events. This includes the quantification of ABL tropospheric coupling and the connection between coupling and regions of convection initiation and intensity.

An interesting way to study the impact of the land surface on convection in models are land cover change experiments. They allow to investigate the sensitivity of the simulated boundary layer and the development of convective events to the external land surface parameters.

Land heterogeneity influences cloud and precipitation initiation and evolution, on the regional and on the climate scale. This is due to its strong local influence on partitioning of fluxes of carbon, water and energy. While computation challenges still exist to explicitly represent this heterogeneity in regional and climate models with finer grid resolution, its effects on boundary layer evolution needs to be better understood and parameterized for coarser grid resolutions currently being used.